1. Field of the Invention
This invention relates to an automatic transmission for an automobile, wherein a preload of a given level is exerted on antifriction bearings supporting an output gear.
2. Description of the Prior Art
With increase in a duration of time during which an engine is run in a high speed mode, a demand for an automatic transmission with an overdrive device is increasing, for improving a fuel consumption efficiency as well as reducing noise. In an automatic transmission for a front-engine, front-wheel drive automobile, intended to reduce weight of the automobile itself, it is desirable to provide an engine with the crank shaft extending transversely of the automobile. To this end, the axial length, of the automatic transmission must be reduced.
An automatic transmission having a reduced axial length has been proposed in co-pending, commonly-assigned U.S. patent application, Ser. No. 06/031,778. That automatic transmission includes a housing containing planetary gear systems respectively including at least three revolving elements, such as a ring gear, a sun gear and a carrier, an input shaft coupled to one of the revolving elements of the planetary gears, and an output gear coupled to another of the three revolving elements of planetary gears and rotatably supported by the input shaft through the medium of a first antifriction bearing means consisting of an inner race, an outer race and a roller. A preload must be applied to the antifriction bearing. For this purpose, in such an automatic transmission, a nut fitted into the end of the housing is turned to be tightened, so as to move the input shaft, thereby changing a gap in the axial direction between the flange portion of the input shaft and the inner projection of the housing, whereby the preload is adjusted. However, adjustment of a preload can not be accomplished unless components are set in given positions within the housing, for example, unless the overdrive device is set in place. Furthermore, in the aforesaid automatic transmission, it is nearly impossible to measure the dragging torque of an antifriction bearing which must be known in order to determine whether a proper preload is exerted on the antifriction bearing. Even measurement of a dragging torque is possible, inaccurate results are obtained.